1. Field of the Invention
This invention relates to a solid-state imaging device and a method of manufacturing the same and more particularly to a solid-state imaging device introducing light to photo-receiving portions formed on a substrate through a light guiding member and a method of manufacturing the same.
2. Background Art
Recently, installing digital cameras on mobile terminals such as mobile phones is generalized. Such imaging devices of digital cameras are required to be low in power consumption and to be small in size. CMOS (Complementary Metal Oxide Semiconductor) type area sensors are receiving attention as imaging devices meeting these requirements.
In a CMOS type area sensor, photo-receiving portion being comprised of a photodiode or the like, a charge detecting circuit, a amplification circuit and a noise reduction circuit and all are formed on a surface portion of a silicon substrate, thereafter a multi-wiring layer is formed on the silicon substrate and a trench is formed directly above a region of the photo-receiving portion in the multi-wiring layer, and then a light guiding member for guiding light into a photo-receiving portion is placed in the trench. Furthermore, the multi-wiring layer has wiring layers having about 2 to 3 layers and an interlayer between wiring layers is insulated by an interlayer insulating film.
When the CMOS area sensor is downsized to increase a number of pixels of the digital camera like this, the area of each photo-receiving portion inevitably becomes smaller. On the other hand, to prevent a signal delay in wirings and mixing of noise, providing enough distance between wiring layers is necessary and a definite height is required for multi-wiring layers. As a result, aspect ratios of the trench increase along with downsizing of sensors. When aspect ratios of the trench increase, light incident at an angle into the trench goes into the multi-wiring layer from the side wall of the trench and is reflected by wirings arranged in the multi-wiring layer, and then becomes harder to arrive at the photo-receiving portion. Therefore, downsizing sensors causes effective introduction of light into the photo-receiving portion to be difficult.
Thus, there is a proposed technology of collecting effectively light incident into the trench to the photo-receiving portion by formation of an empty space (air layer) between the side wall of the trench and the side surface of the light guiding member and reflecting the light at an interface between the light guiding member and the air layer (for example, see JP 06-224398A and JP 2003-060179A). In technologies described in JP 06-224398A and JP 2003-060179A, the empty space is formed between the side wall of the trench and the side surface of the light guiding member by forming a dummy layer on the side wall of the trench and then removing the dummy layer after forming the photo-receiving member.
However, in technologies described in JP 06-224398A and JP 2003-060179A, a complicated process is needed for formation of the empty space as described above, thus productivity of sensors is low. Moreover, since process errors are accumulated every process, shape stability of the empty space is low.